This invention relates to a brake hydraulic pressure control unit for use in a vehicle for increasing and reducing brake hydraulic pressure using electric signals.
A conventional such brake hydraulic control unit is disclosed in JP patent publication 8-502007.
The brake hydraulic pressure control unit disclosed in this patent publication includes a housing in which is mounted a pump, a hydraulic fluid reservoir, hydraulic pressure control valves, and a motor for driving the pump. The pump draws hydraulic fluid in the reservoir and returns it to the brake line. The electronic control unit controls the brake pressure by selectively supplying hydraulic fluid into the hydraulic circuit (for pressure increase) and discharging hydraulic fluid into the reservoir (for pressure reduction) by opening and closing the hydraulic pressure control valves.
The brake hydraulic pressure control unit disclosed in JP patent publication 8-502007 includes a pulsation damper disposed between the discharge port of the pump and the hydraulic circuit for muffling the pump operation noise.
The reservoir and the pulsation damper are formed integrally with the housing. Specifically, as shown in FIG. 10, the reservoir comprises a bore 2 as a fluid chamber which is formed in the housing 1, a reservoir piston 3 inserted in the bore 2, a cover 4 coupled to the housing 1, and a spring 5 disposed between the reservoir piston 3 and the cover 4 for biasing the reservoir piston 3 to move it in such a direction that the volume of the fluid chamber decreases.
All the other conventional brake hydraulic pressure control units also have their reservoir formed as an integral part of the housing. Such an integral reservoir makes it difficult to reduce the size and cost of the entire unit for the following reasons.
If a plurality of reservoirs of such brake hydraulic pressure control units have lengths substantially equal to one another, their capacities are proportional to the square of their diameters and proportional to their piston strokes. Thus, if the capacity of the reservoir is fixed, as such a reservoir, one having a greater diameter and a shorter length should be selected in order to reduce the size of the brake hydraulic pressure control unit to a minimum. But a reservoir having a large diameter increases the depth of the housing 11 (dimension shown by “S” in FIGS. 10 and 11).
Conversely, if a reservoir having a greater length and shorter diameter is used while keeping its capacity unchanged, the height H of the housing will increase. The numeral 7 in FIGS. 10 and 11 indicates a pump-driving motor fastened to the housing.
The width w of the housing 1 is determined by the pitch of pipe connections (not shown) provided on the top 1a of the housing 1. Thus, if the depth s and/or height H is large, each side 1b naturally has a correspondingly large area. Such a housing is large in size.
The minimum value of the capacity of the reservoir is determined by the structure of the vehicle on which the brake hydraulic pressure control unit is to be mounted. The minimum value of the capacity of the reservoir in turn determines the minimum size of the housing as described above. Thus, if it is desired to use a housing having the allowable minimum size for the vehicle on which the control unit is to be mounted, a large number of housings that are different in type and size from one another have to be prepared according to vehicle types. One way to avoid this problem is to use uniform housings which can accommodate the largest reservoir. But such housings are unnecessarily too large to accommodate smaller reservoirs. Preparing a large number of housings that are different in size from one another and preparing uniform but oversized housings are both economically unfavorable.
For the pulsation damper, too, which is optionally provided as necessary, the greater its capacity, the more effectively it can damp pulsation. But if the damper, which is also an integral part of the housing as with the reservoir, is unnecessarily large in size, the size of the housing will also have to be unnecessarily increased, which pushes up the cost of the entire control unit.
If the size of the housing is reduced to a minimum, it will be difficult to increase the capacities of the reservoir and the pulsation damper even slightly.
An object of this invention is to provide a low-cost, compact brake hydraulic pressure control unit comprising a housing and a reservoir and optionally a pulsation damper in which the size of the housing can be determined irrespective of the capacities of the reservoir and the pulsation damper.